The present invention relates to door operating devices and more particularly to a motorized swinging door apparatus having a spring loaded door closing mechanism.
There are many closure applications wherein a pedestrian door is opened often to facilitate passage therethrough yet should remain closed most of the time. To this end the door industry has configured many different types of automatic opening/closing systems. One exemplary system for opening and closing a swinging door is described in U.S. Pat. No. 4,333,270 which is incorporated herein by reference. That system includes an activation mechanism, a motor, a gear box, a shaft, an arm and a helical spring. The gear box typically comprises three or four gears arranged to form a gear train. The gears include first and last gears at proximal and distal ends of the gear train, respectively. The last gear is typically a piston type gear such that when other gears are rotated, the piston gear is driven linearly. The shaft includes gear teeth at least a proximal end and the piston gear includes linear teeth for engaging the shaft teeth, the shaft rotating when the piston gear is driven linearly.
The motor is linked to the first gear at the proximal end of the gear train such that when a motor rotor rotates, the gears cause the piston gear at the distal end of the gear train to move linearly thereby rotating the shaft. The gears are designed so that motor force increases along the gear chain. The arm is linked at one end to the shaft and at another end to the door and can be forced between open (i.e. wherein the door is open) and closed (i.e. wherein the door is closed) positions. The spring is linked to the last gear and biases the last gear, shaft and arm into the closed position. Typically the spring operates over only a small operating range (e.g. less than 4 inches). The activation mechanism, typically a foot pad, microwave or infra-red sensor, is linked to the motor.
When a pedestrian is sensed by the activation mechanism (e.g. the pedestrian steps on the foot pad or enters the space monitored by the sensor), the motor is excited. When the motor is excited, the motor forces the gears to rotate, the piston gear forcing the arm and door into the open position against the spring force. When the door is opened, the spring is compressed and mechanically loaded. When the motor is turned off or is driven in the opposite direction, the spring decompresses and forces the door closed. If, during a period when the door is closing, a pedestrian again activates the activation mechanism, the motor is again excited and the door is forced open against the spring force.
According to another design, instead of using a helical spring which operates on a last piston-type gear adjacent the shaft, a torsion spring (i.e. similar to a watch spring) has been used in conjunction with a last round gear to effect door closure. In this case, the shaft extends axially from the last round gear and the spring forces rotation of the gear and associated shaft in a closing direction when power is removed from an associated motor. When the motor is turned on the motor compresses the spring as the last gear and shaft cooperate with an arm to open the door. In this case, the torsional spring typically only rotates through approximately 135 degrees between opened and closed spring positions. An example of this type of apparatus is described in U.S. Pat. No. 4,045,914 which is incorporated herein by reference.
For safety purposes, spring and gear systems like those described above are rendered inaccessible to pedestrians by providing a housing around the entire system which is only removed during installation or maintenance.
While most automatic swinging door systems have components and operate as described above, most system manufacturers provide several different system configurations having the general characteristics described above to facilitate door operation, each configuration designed to accommodate a unique set of environmental constraints. For example, the system configuration required to cause a door to open inwardly is different than the configuration required to cause a door to open outwardly. In addition, the system configuration required to open a door inwardly which is hinged along a right hand door edge is different than the configuration required to open a door inwardly which is hinged along a left hand edge.
While each of the systems above operate to open and close a door, each system suffers from several shortcomings. First, because the spring is linked to the last gear in the gear train, the spring has to be chosen such that it can overcome the full weight of the door in addition to gear friction to effect closure. In addition, in certain applications it is necessary to provide a spring capable of even more force than that required to overcome door weight and gear friction to close a door. For example, where an outside door opens inwardly and is located in an area prone to relatively high wind, the spring also has to overcome the wind force on the door to close the door. Similarly, in climates where snow can be expected the spring force may have to overcome some snow blockage at the base of the door during closure. Where environmental factors can be expected to periodically hinder door closure, springs which store extra force are provided.
In these configurations, while the spring will cause a door which is impeded to a maximum degree to close at an ideal rate, when the door is unimpeded or is impeded at less than the maximum degree and the motor is turned off the spring will distress rapidly closing the door at a faster than ideal rate. Rapid closure can cause door damage and/or can injure a pedestrian within the range of door motion.
For this reason, to provide an ideal spring distressing rate and hence door closure rate which is independent of environmental conditions, the motor is often used to control spring distressing which in turn regulates door closure speed. To this end, assuming clockwise motor rotation opens a door, the motor is driven in a counter-clockwise direction during closure and at a rate which is slower than the rate at which the spring alone would close the door. This type of motor control is often referred to as braking as it effectively brakes the rate of door closure.
Despite large spring force requirements, the space provided for the system spring is extremely limited for both practical and aesthetic reasons. As indicated above, typical helical springs are only approximately twelve inches in length. Torsional springs are typically less than four inches in diameter. Such springs are relatively expensive and usually, to meet the force and space criteria, have to be designed close to their material failure limits. Springs designed close to their material failure limits are more likely than more robust springs to fail which increases component and maintenance costs over the useful life of the system.
Second, none of the systems described above is easily reconfigurable to accommodate different environmental constraints. Where a system is used with a right-hand-hinged inwardly opening door, the system cannot easily be reconfigured for use with a left-hand-hinged inwardly opening door or either a right-hand-hinged or left-hand-hinged outwardly opening door. This is particularly problematic where environmental constraints are changed and different door opening characteristics are required.
In addition, these systems cannot be reconfigured such that the spring opens the door and the motor closes the door. While most applications favor a door which is driven open by the motor and is forced closed by the spring, there are applications where the opposite is advantageous where the motor closes the door and the spring opens the door. An example might be an interior office with an inwardly opening door where there are no windows to provide natural light. Upon power loss which may occur during an emergency, the above systems close the door leaving an office occupant in the dark and forcing the occupant, after locating the door, to pull the door open against the spring force to exit.
Moreover, the springs in these systems cannot be easily replaced for maintenance purposes or to change the spring force to accommodate different environmental constraints. For example, as indicated above, some doors may be located in a relatively windy environment while other similarly configured doors are not. While a high stress spring may be required for door closure in the windy environment, the high stress spring may not be required in another environment. In this case, it would be advantageous to have a configuration which allows an installer to select and easily install the spring required for the system thereby minimizing system costs. In fact, it would be advantageous to have a system wherein, if desired, the spring could easily be removed from the configuration and the motor alone could be used to open and close the door.
Therefore, it would be advantageous to have an automatic swinging door system which requires a relatively inexpensive spring which is both relatively small, is well within material limit constraints and which can still provide a large force for closing a door, wherein the system is easily configurable to accommodate many different environmental constraints.